A communications system is a facility which enables communication between two or more entities such as user terminal equipment (mobile or fixed) or other communication device, network entities and other nodes. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on.
An appropriate communications network provides a user with a access to the communications system. A communication device of the user may be capable of accessing a communications system by means of a plurality of different access networks, this requiring that the communication device is compatible with different access technologies.
A communications network typically operates in accordance with a given standard or with a given set of specifications which set out what the various elements of a system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched bearer or a packet switched bearer, or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner in which communication should be implemented between the user equipment and the elements of the communication networks is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication can be based needs to be defined to enable the user equipment to communicate via the communications system.
An access interface may be provided by a fixed line or wireless communication interface. Communication systems providing wireless access enable at least some degree of mobility for the users thereof. More advanced mobility support can typically be added as an enhanced feature. An example of communication networks providing wireless access is a public land mobile network (PLMN), such as the second generation (2G) GSM (Global System for Mobile communications), the so called 2.5 generation GPRS (General Packet Radio Service) or the third generation (3G) WCDMA (Wideband Code Division Multiple Access) or EDGE (Enhanced Data for GSM Evolution). The public land mobile networks (PLMN) are commonly based on cellular technology.
In cellular systems, a base transceiver station (BTS) or similar access entity services mobile communication device or user equipment (UE) via a wireless interface between these entities. The communication on the wireless interface between the user equipment and elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. Other examples of wireless access technologies include various wireless local area networks (WLANs) and satellite based systems.
Examples of fixed line access technologies include public switched telephone networks (PSTN), cable networks, digital subscriber line (DSL) networks, and so on.
The various control entities of a communication system may be interconnected. One or more gateway nodes may be provided for connecting an access network to other communication networks, for example to an IP (Internet Protocol) and/or other packet switched data networks. In such arrangements, the communications network provides an access network enabling a user with appropriate user equipment to access external networks, hosts, or services offered by specific service providers.
In a packet data network, a packet data carrier or bearer may be established to carry traffic flows over the network. An example of such a packet data carrier is a packet data protocol (PDP) context in current GPRS, EGPRS and WCDMA networks.
Conventional mobile terminals may support only cellular access technology for data communication, and usage of data in those mobile terminals is relatively simple. For example, in response to a user launching a data application a pre-defined GSM data connection, a GSM based EDGE data connection, or a WCDMA data connection or similar may be created.
More sophisticated user equipments provided with multi-radio capabilities may access services provided via the communications system via a number of access network technologies. For example, a mobile device may connect to services provided via the communications system by setting up a PDP context on an EDGE network of a 3G access network, or by setting up a connection through a non-cellular complementary access system, for example a WLAN.
This means new opportunities for data transfer, for example for applications like Voice over the IP (VoIP). On the other hand, this also causes new challenges, for example, because of introduction of mobile applications that need to be processed by the cellular and non-cellular systems with changing characteristics for the access, for example the bitrate, cost, coverage and so on. For example, cellular coverage is typically provided nationally whereas WLAN coverage is only provided in small hot spots. Therefore cellular connectivity should work all the time but non-cellular systems, for example the WLAN, provide only temporary and local connectivity. Because of the different nature of the access systems substantially different features such as networking protocols and applications may be used by the different access technologies.
The number of increased access technologies, the temporary availability of some access technologies, for example the WLAN, and variety of applications with different requirements increase mobile terminal usage complexity and might lead to under-usage of network potential. For example, it may turn out to be laborious to try to activate a WLAN connection because a user might not know where a WLAN hotspot is available.
If decisions that relate to connectivity are not automated, usage of mobile terminals may become fairly complex, thus hindering utilization of the potential different connectivity technologies may offer. For example, a user may wish to use a WLAN access for email communication when there is no WLAN facility available. In such situation the user may stay on a GPRS (General Packet Radio Service) network for a considerable time, even for days, unless he/she continuously checks for the availability of a WLAN network or similar. If the connectivity decision is automated, the mobile communication device could automatically switch to a WLAN network after detection that such a network has become available.
However, if a mobile terminal is enabled to select an access technology automatically, then other problems may arise. This may be the case especially in association with protocols used in different networks to access services. For example, although a set of protocols might be enough when using a GPRS connection, another set of protocols might be needed when using a WLAN connection. If the WLAN access is provided by a WLAN network that does not offer enabled security features better security may be required on the IP level (like IPsec) to prevent evesdropping. An average user may have difficulties if he/she tries to manage all the required settings manually. Therefore it might be advantageous to have an improved mechanism for selection of an access interface.
As well as selecting an access interface, a terminal may need to select a source address for data packets to be transmitted according to a communications protocol. For instance, in certain circumstances, the terminal may be able to choose between sending packets via a home address as source address (reverse tunnelling via a home agent) or sending packets directly to a Correspondent Node (CN) using Care-of-Address (CoA) as source. Further selection options may be available where the terminal has a plurality of home addresses in use. Current protocols may be insufficient to deal with such situations.